Outlier of a group

Layman, in sense 2 of the Oxford English.

Alternatively, and only very informally, "explain like I'm five" means "explain in simple terms" (where "five" here means "five years old").

"Put it in layman's terms for me."

in layman's terms ODOL
phrase

Phrased so as to be easily understood, without the use of technical or obscure terms.
‘They will explain things in layman's terms and work with you to not only help you reach the top but understand how you got there as well.’

(Layman has already been suggested by Patrick Stevens.) See MW "Layman: a person who does not belong to a particular profession or who is not expert in some field"; "Layman's terms: simple language that anyone can understand The process was explained to us in layman's terms."